This invention relates to the separator of particulate glass, and is particularly concerned with procedure for the color sorting of multi-colored glass particles in particulate glass, especially particulate glass recovered by froth flotation from shredded municipal trash or waste, by procedure which involves differential heating of particles of glass of a preselected color or colors, by light absorption of such glass particles, and contacting such glass particles with an organic thermoplastic material in the form of a coating on the glass particles or on a separate surface, causing melting of such organic thermoplastic material in contact with the thus differentially heated colored glass particles and permitting separation thereof from the remaining glass particles as by flotation or adhesion.
Although the particulate glass recovered by froth flotation from shredded municipal trash can be made clean enough for recycling, wide adoption of such process is limited because the particulate glass is generally of mixed colors. Thus, for example, particulate glass thus obtained and contaminated with relatively small amounts of green glass, e.g. of about 5 to about 8%, can only be melted to a green or amber glass. Substantially the only use for green glass as made in a furnace appears to be for bottles, which is only approximately 10% of total bottle production. For all other uses of green such as for pressware, e.g. glasses, salad dishes, novelties, and the like, the green glass is made by forehearth addition of pigments to the otherwise flint cullet, and is generally made between large production runs. Thus, the color is added after the glass is made, and only to the quantities of glass needed for the particulate item or items.
Although it was found that particulate glass can be color-sorted by magnetic separation, an economically feasible method employing this principle has not as yet been developed. Other magnetic sorting approaches using paramagnetic fluids to establish magnetically sensitive density gradients have also been tried without success.
It is accordingly a particular object of the present invention to provide novel procedures and systems for efficiently sorting particulate colored glass, especially colored glass obtained by froth flotation of municipal waste, to obtain a relatively clean separation of one or more preselected colors of the particulate glass in the mixture, from other colored glasses present.